Air temperature sensors inside the cabin of an automobile are used to obtain a measurement of the room temperature inside the cabin of an automobile. However, in some situations, the air temperature value obtained from the air temperature sensor is not necessarily indicative of the room temperature of the air inside the cabin of the automobile.
Causes of inaccuracy in the determination of room temperature include, but may not be limited to, heat sources near the sensor, heat capacitance of nearby objects, outlet temperature air flowing into the sensor and even sun load striking the sensor location.
Differences between the actual room temperature and the air temperature value obtained from the temperature sensor may be present for a number of reasons, one of which is that the air that is used by the sensor to obtain the temperature reading may exchange heat with mass surrounding the temperature sensor. For example, if the temperature sensor is located underneath a dashboard and the material of the dashboard is at 100 degrees F. (because, for example, the car has been sitting in a hot garage during the summer) but the room temperature of the air inside the cabin is 70 degrees F. (because, for example, the air conditioner, which has recently been started, has been operating to deliver cooler air inside the cabin), the air immediately surrounding the temperature sensor (i.e., air that is used by the sensor to obtain a temperature measurement) may be at a temperature in between the room temperature (70 degrees F.), and the temperature of the dashboard (100 degrees F.), because as the air from the cabin moves over the dashboard and into the temperature sensor, heat from the dashboard is exchanged with the air, resulting in an increase in temperature of the air sampled by the sensor from the room temperature value.
As noted above, the temperature of the air that is used by the temperature sensor may also be different from the actual room temperature value because the air sampled by the temperature sensor may, in actuality, be a blend of air at the room temperature of the automobile (that is, in the example given above, 70 degrees F.) and air at a temperature of the outlet temperature of air leaving the conditioned air outlet vent. That is, for example, in instances where an outlet vent in the automobile is supplying conditioned air to the cabin at a temperature that is different from the actual room temperature, a portion of this conditioned air may find its way directly to the temperature sensor, thus influencing the temperature reading of the temperature sensor. By way of example, if air is being directed into the cabin at 60 degrees F., the air sampled by the air temperature sensor may include both air at 70 degrees F. (the room temperature) and air at 60 degrees F. (the outlet temperature).
Automatic climate control systems require reliable accurate information regarding the vehicle cabin interior temperature, in order to achieve the occupant's comfort objectives. The above discussed corrupting influences present challenges in appropriately reaching and maintaining target comfort levels in the vehicle.
Symptoms of these problems include room temperature over-shooting (passing the target), drifting of the interior temperature during long driving, poor warm-up and cool down rates.
Thus, there is a need to more accurately determine the room temperature in a cabin of an automobile by addressing the effect of various thermal influences on a temperature sensor.